Chemical-mechanical polishing (“CMP”) processes are used in the manufacturing of microelectronic devices to form flat surfaces on semiconductor wafers, field emission displays, and many other microelectronic substrates. For example, the manufacture of semiconductor devices generally involves the formation of various process layers, selective removal or patterning of portions of those layers, and deposition of yet additional process layers above the surface of a semiconducting substrate to form a semiconductor wafer. The process layers can include, by way of example, insulation layers, gate oxide layers, conductive layers, and layers of metal or glass, etc. It is generally desirable in certain steps of the wafer process that the uppermost surface of the process layers be planar, i.e., flat, for the deposition of subsequent layers. CMP is used to planarize process layers wherein a deposited material, such as a conductive or insulating material, is polished to planarize the wafer for subsequent process steps.
In a typical CMP process, a wafer is mounted upside down on a carrier in a CMP tool. A force pushes the carrier and the wafer downward toward a polishing pad. The carrier and the wafer are rotated above the rotating polishing pad on the CMP tool's polishing table. A polishing composition (also referred to as a polishing slurry) generally is introduced between the rotating wafer and the rotating polishing pad during the polishing process. The polishing composition typically contains a chemical that interacts with or dissolves portions of the uppermost wafer layer(s) and an abrasive material that physically removes portions of the layer(s). The wafer and the polishing pad can be rotated in the same direction or in opposite directions, whichever is desirable for the particular polishing process being carried out. The carrier also can oscillate across the polishing pad on the polishing table.
In polishing the surface of a workpiece, it is often advantageous to monitor the polishing process in situ. One method of monitoring the polishing process in situ involves the use of a polishing pad having a “window” that provides a portal through which light can pass to allow the inspection of the workpiece surface during the polishing process. Such polishing pads having windows are known in the art and have been used to polish workpieces, such as semiconductor devices. For example, U.S. Pat. No. 5,893,796 discloses removing a portion of a polishing pad to provide an aperture and placing a transparent polyurethane or quartz plug in the aperture to provide a transparent window. Similarly, U.S. Pat. No. 5,605,760 provides a polishing pad having a transparent window formed from a solid, uniform polymer material that is cast as a rod or plug. The transparent plug or window typically is integrally bonded to the polishing pad during formation of the polishing pad (e.g., during molding of the pad) or is affixed in the aperture of the polishing pad through the use of an adhesive.
Typically, windows are mounted into the top polishing pad layer and are either flush with the top polishing surface of the polishing pad or are recessed from the polishing surface. Windows that are mounted flush can become scratched and clouded during polishing and/or during conditioning resulting in polishing defects and hindering endpoint detection. Accordingly, it is desirable to recess the window from the plane of the polishing surface to avoid scratching or otherwise damaging the window. Polishing pads having recessed windows are disclosed in U.S. Pat. Nos. 5,433,651, 6,146,242, 6,254,459, and 6,280,290, as well as U.S. Patent Application No. 2002/0042243 A1 and WO 01/98028 A1.
Conventional methods for affixing a window into a polishing pad typically involve either the use of an adhesive to attach the window to the pad, or an integral molding method. Such conventional methods produce polishing pads which suffer one or both of the following problems: (1) the seal between the polishing pad and the window is either imperfect or deteriorates during use such that polishing slurry leaks through the polishing pad and onto the platen or behind the window thus compromising optical clarity for endpoint detection, and (2) the window may separate from the polishing pad during use and be ejected.
Thus, there remains a need for an effective polishing pad comprising a translucent region (e.g., window) that has improved wear resistant properties and can be produced using efficient and inexpensive methods. The invention provides such a polishing pad, as well as a method of its use. These and other advantages of the present invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.